Expand "Authoring Guide"

## About

Going forward, the "Authoring Guide" wants to absorb more content, to maintain it all in a single place, and provide it nicely rendered.

- https://crate-docs-theme.readthedocs.io/en/latest/authoring.html

## Details

- Style Guide from `crate-docs:style/*.rst`
- Guidelines about utility support, e.g. about `linksmith`

## References

- https://github.com/crate/crate-docs/tree/main/style
- https://github.com/crate/crate-docs/issues/105
- https://github.com/crate/cratedb-guide/issues/372
- https://github.com/crate/tech-writing/blob/main/README.md
- https://github.com/crate/crate-docs-theme/blob/main/DEVELOP.rst